Glass treatment



May 22, 1934. H, R, MQULTQN 1,960,121

GLASS TREATMENT Original Filed Feb. 10, 1930 f f l l l l f l HGM /qnl/7.]Z%,ENTOR Dfi/7mo i?. /VodLTo/v Y ATTORNE Patente-.1MM 22, i934V i igolzl errno ,STATESPATE'NT OFFICE 1.960.121 v GLASS TREATMENT Harold R.Moulton, Sturbridge, Mass.,` assigner to American Optical Company,Southbridge. Mass., a voluntary association of Massaclnpl setts rApplication February 10, 1930; Serial No.v427,202

Renewed lilovembcr 10, 1932v This invention relates toimprovementsinglass in oil, air or steam. IIlhis method produced atreatment and has particular reference to the thin skin of hardenedglass Von the Surface, but Vit process of producing strengthened glassand to will be apparent that this thin skin could be easily the productof said process. removed if any surfacing-or polishing process was Theprincipal object of this invention is to procarried out after thehardening. This greatly 69 vide a glass composed of layers havingdifferent restricted the use of this method as articles such coeicientsof expansion to lend strength thereto as lenses had to be finishedbefore hardening and and also having similar indices of refraction thensubjected t this PIOCSSS Which invariably throughout the layers toproduce good denition ,spoilt their definition by Causing blenliSheS andi1- or no distortion of objects viewed therethrough. regular indexChanges and Often bIOke them en- 65 Another object of this invention isto provide tirely from the Sudden Cooling and because of nmeans wherebyarticles requiring a high surface. terna-1 StrainS- It WaS PracticallymDOSSihie t0 ilnish and good definition of image such as lenses, produceophthalmic lenses by this process or any may be nished afterstrengthening without in article requiring a Clear Visual bodyl5 anydetracting from their strength. The other prior art method ofstrengthening 70 Another object of this invention is to provide glasscomprised Securing together two or more means whereby the said improvedglass maybe layers of glass having different coefficients oi exmade by aprocess having simple and familiar Vpansion.A vThe theoryunderlying thismethod was steps. l that the layer of glass having the higher coefii-Another object of this invention is to eliminate cient Of expansionWould Shrink (when the tem- 75 the breakage and poor .quality Aofarticles made perature dropped after uniting i211e layers by heat) bythe usual strengthening processes.' more -than the layer having thelower coefficient Other objects and advantages will become ap Vofexpansion-so that one layer would be in tension parent from thefollowing description taken in' andthe Otherincompression. Any blow orsudden connection with the accompanying drawing and temperature changereceived on the side under 'S0 it will be apparent that many changes maybe compression was withstood much better than it made in the details ofconstruction, arrangement would have been if the glass 0n that Side WaSof parts and steps in the process without depart. not under compressionor ii it was under tension, ing from the spirit of the invention asexpressed Since' it iS Weil knOWn that glaSS under Compresin theaccompanying claims, I therefore, do not sion Oilers greater resistanceto sudden heating 85 wish to be limited to the exact details shown andor cooling or mechanical shocks than one under described as thepreferred forms only have been tension or without compression. shown `byway of illustration. This process was satisfactory where the glass Inthe drawingz v was not used for visual purposes and it made satis- Fig.I is a sectional view of one form of my factory boiler' sauge tubes,lamp chimneys and 90 invention. y cooking vessels. As the indices ofrefraction of l Fig. II is a sectional view oi' a modified form. the4different glass layers were not controlled Fig. III is a sectional viewoi further modifica-r however, the effect upon looking through suchtion. l glass was much the same as that of a. multifocal 4.0 Fig. IV isa sectional view of an alternative lens, since the various kinks andbends formed 95 method of accomplishing the modiiication shown powercurves due to the diierent indices oi rein Fig. III. fraction and thesedestroyed all denition oi ob- Fig. V is a sectional View of a furthermodicajects Viewed therethIOugh. tion of the method shown in Fig. III.It is the prime 'object of my invention, there- Fig. VI is adiagrammatic sectional view illusfore, to combine the advantages of thislatter 100 trating an exaggerated strain in compound glass. process inregard to strength and at the same Fig. VII is a perspective view of amodified time combine good definition ci objects therewith.

method of fusing two layers of glass together. This combination ofadvantages renders this im- Fig. VIII is a perspective View illustratinga proved glass oi wide application inasmuch as'any 5o modification ofthe process shown inFig. VII. glass article may be made therefrom whensaid 105 Prior to my invention there were two principal article is to beused between thel eyeand anobject 4methods of strengthening glass, bothof which lor for the projection of images or for any other wereunsatisfactory from various standpoints. use necessitating clear visualqualities in the glass. One of the methods consisted in heating theReferring to the drawing the numeral l denotes glass and quenching it byvarious means such as a layer of glass of one index of refraction and11.0

one coefllcient of expansion. Secured to this layer 1 is a second layer2, having a similar index of refraction as glass 1 but having a highercoeicient of expansion. It will be understood that the indices O frefraction and the coeflicients of expansion may be of any desiredvalues;A As is vratio of thickness must be high. The layer of lowercoemcient of expansion is, under this rule, always the thinner of thelayers, as in Fig. 1, where numeral 1 denotes the lower coeicient layer.

By controlling the indices of refraction of layers 1 and 2 it will beapparent that novel means have been provided to produce strengthenedglass having good definition and suitable for use where clear visualqualities are to be combined with resistance to temperature changes andsudden shocks. This glass can also be nished after hardening as there isno risk of removing a thin skin as in quenched glass and it is muchcleaner and superior in every way to quenched glass.

In the manufacture of this'. improved glass the well-known process ofmaking case glass is preferably utilized, although other methods, suchas fusing, may be used if desired.

In the case glass process the glass for the layers -1 and 2 is made indifferent crucibles, one glass having a lower coefficient ofexpansionthan the other and both having similar indices of refrac` tion. Glassfrom one crucible is gathered 'and blown and then cased with the glassfrom the other crucible after which the blown cylinder may be cut intostrips, flattened and cut to shape.

This process is the usual one for case glass, but the control of theindices of refraction` to obtain the desired result is, as far as I amaware, novel to my invention.

The glasses 1 and 2 are united while soft so that at that temperature nostrain exists. As the temperature Idrops, glass 2 of higher coeicient ofexpansion shrinks more than glass 1, of lower coemcient of expansion.This puts glass l in compression and glass 2 in tension. Any blowrecelved upon glass 1 is withstood far better than if this side was notunder compression or was undertension which follows the well-known ruleregarding strength in glasses. d

If the glass is to be used for lenses, windshields or other articleswhere strength to resist shock must bey combined with good visualqualities, the strengthened' glass may be cut to desired shape, surfacedto any curvature and polished to any degree required. Owing to thesimilarity between the indices of refraction of the layers any slightwaves or irregularities will not destroy denition,

as they would do if the indices are different and' not controlled. q

In mounting articles such as lenses or windi shields the glass 1 undercompression. is faced towards the side exposed to the hazard of iiyingmissiles as will be apparent. This glass may be curved or-shaped in anymanner depending upon' the required shape desired.

' As a modification I can combine as many layers of glass as desired andas shown in Fig. 1I. I' can unite three such layers. The4 two outerlayers 3 facility as the casing process.

' Y By reference to Fig. III it will be clear that the control of thesoftening point is an advantageous and 5 are preferably of lowercoemcient of expansion than the inner layer 4, although'all the threelayers are preferably of similar index of refraction. This type ofconstruction will readily bear the brunt of shocks on both faces 3 and 5and is made similarly tothe method outlined for the type illustratedin'Fig'. I.

If it is more desirableto fusevinstead of casing the glassestogether-other factors enter into the requirements and I have providednovel means of accomplishing the fusing process with as much The indiceslofrefraction of the glasses used should, of course; .remainsubstantially equal, but inaddition therefshould be a difference in thelfusing or softening points of the glasses which will facilitate theoperation and give a better product. It will be understood, therefore,that for fused compound glass I prefer to control three factors, e. g.,the coeflicients of expansion, the indices of refraction and thesoftening or fusing points.

feature of the fusing process. The glasses 1 and 2 are placed on arefractory block 6 and Then fused together glass 1 will lbe incompression and glass 2 in tension as described in the casing process. Iprefer that the glass 2 under tensionl should have a fairly highsoftening point in order that the surface in contact with thelrefractory block 6 will not become plastic enoughbefore fusing to bemarred by the refractory block or to sag if the glasses are supportedonly atftheir edges as shown in Fig. IV. The glass 1 to be undercompression is preferably of a lower softening 11u or fusing point thanthe glass 2 in order to accomplish the l advantageous results stated. Itwill be understood that the indices ofrefraction and the coefficients ofexpansion remain as before, but with the additional factor of control ofthe softening or fusing points of the glasses.

Pursuingthe foregoing rule Ifmay in fusing a three component article,asshown in Fig. V where glasses 3 and 5 are to be in compression andglass 4 in tension, contrive that the softening or 120 fusing points aregraded from high to low from the bottom glass 5 to the top glass 3.Hence, glass 5 will have the highest fusing point, glass 4' intermediateand glass 3 of low fusing point.

This arrangement holds good for any number 12,5 of'layers if it beremembered that the glass nearest the refractory block 6 should have thehighest fusing point of the component glasses used. AIn regard to thelatter process of fusing a three component article I have found thatthis con- 13u struction is to be preferred to the two component particle where large surfaces are secured together.

It is known that the tendency. of a composite plate of two glassessecured together is to warp and curve towards the side under'tension asshown in 135 Fig. VI, so that this side becomes a concave curve insteadof remaining flat. .In lenses orI other articles of a small nature thiswarping isnegligible, but it is desirable on large articles to preventthis. I have found that by utilizing a three com- 143 ponentconstruction as in Fig. II this warping is prevented. It is obvious thatwhen, as in Fig. DI, the compression of glasses 3 and 5 is equal on bothsides of the middle glass 4 which is in tension, no warping can result.This equal compression of glasses 3 and 5 may be obtained always unlessthere is a great disparity between the coeicients of expansion orthickness of glasses 3 and 5. In Fig. VII I have illustrated a method bywhichthe fusing of two layers may be accom- 15o layer combination and itwill be apparent that any number of layers may be secured together inthis manner.

In utilizing this novel method and in reference to Fig. VIII preferablyhave the lower layer 2, as before, of a higher softening point andhigher coefficient of expansion than the upper layer 7.

The indices of refraction of the two layers 2 and 'I are, of course,similar. The upper layer 'l is preferably curved so that a line contactisobtained at8 with the lower layer 2 which rests on the usualrefractory block 6. When, under heat, the upper layer 7 of lowersoftening point wilts and drops, it will do so from theline 8 outwardsand the air between the layers will' be expelled from the line 8outwardly until the terminal ends 9 of the upper layer '1 eventuallyreach and contact with the lower layer 2. This process eliminates thebubbles which usually form between fused surfaces and a far superiorproduct results.

Applying this method to a three layer combination, as shown in Fig.VIII, the lower layer 2 is, as before, of iiat surface and in contactwith the block 6. The layer '7 may be placed, also as before, `upon thelayer 2 and above this the thirdv layer l0. If the layer 10 is made ofgreater curvature than the layer '7 a line contact will be formed at 11.It will be understood that layer 2 is of high fusing point and layers '7and 10 graded in descending values, as previously stated, so that layer10 has the lowest softening or -Iusing point. It will-be obvious,therefore, that layer l0 will first drop from the center line contact 11outwardly and then layer 7 will do likewise, thus eliminating allbubbles from between the contact surfaces. This may be applied to anynumber of layers as will be apparent as long as steeper curvatures areusedfor each additional layer.

The application of this improved strengthened glass is very wide as willbe apparent. Practically any article of glass which is used to lookthrough or have images projected there-through will be v benefitted bybeing strengthened. It will be understood that in the two-layer fusedconstruction the described order may be reversed and glass 1 in Fig.III' may be nearest the block. In this way the side nearest the blockmay be surfaced after strengthening and the other side untouched.' Allthe drawbacks of prior strengthened glass have' been eliminated and'thisuseful strengthening process made available for use on the wide varietyof articles used for visual purposes; In the manufacture of ophthalmiclenses for protection goggles this invention is'of particular merit, in-

asmuch as much time and material have hereto--v fore been devoted toproducing an inadequate and poor product by prior art methods such lasthose described herein.

- compression andI surfacing the two exposed faces lwith each other, theouter layers being of sub- The foregoing description will. clearly showthat'i simple and novel means have been provided td 'carry out' theobjects of the invention and that,

calculated thickness, subjecting the said piece of glass to heat tocause the same to unite and allowing said pieces to cool whereafter oneof said pieces will be in tension and the other will be in of the unitedglass to a smooth polished surfacel 2. The process of formingrastrengthened glass having clear visual characteristics comprisingforming a piece of glass Aof a given index of re-l fraction andcoeiiicient of expansion to a calculated thickness, forming a secondpiec'e of glass l of the same index of refraction asl the rst piece andof a different coeicient of expansion to a cal- Aculated thickness,forming a third piece of glass of the same index of refraction andcoefiicient of expansion as the first piece and to a calculatedthickness, placing the second piece of glass having a differentcoefiicient of expansion betweenthe first and third pieces of glass,subjecting the said pieces of glass to heat to causev the same to unite11o and allowing said ,pieces to cool whereafter the central piece ofglass wil be in tension and the outer pieces of glass will be incompressioxrand`v surfacing the exposed faces of the pieces of glass toa smooth polished surface. v

3. A composite strengthened glass having uniform optical definition atall points throughout its area comprising superimposed layers of glass.one of said layers being in tension and the other in compression. 120

4. A composite strengthened glass comprising layers having substantiallyidentical indices of refraction andpredetermined differences ofcoefficients of, expansion, one of said layers being in tension and theother in compression. 5..A composite strengthened glass comprising threelayers of glass in superimposed relation stantially the same indices ofrefraction and coefdcients of expansion and the inner layer being l ofsubstantially the same index of refraction but of a predeterminedgreater coefiicient of expansion.

HAROLD R. MOULTON. 135

